Evolutionary and attachment-related accounts of relationships
have similar claims about romantic love and sexual desire (e.g.,
Diamond, 2003; Fisher, 1998; Hazan & Shaver, 1987). Romantic
love is thought to be part of a pair-bonding system, which keeps
partners together in long-term relationships that are oriented toward
raising vulnerable, dependent offspring to the age of viability
(Buss, 1988, 1994; Buss & Schmitt, 1993; Fisher, 1998; Kenrick &
Trost, 1997; Simpson, 1994). As a part of the mating system and
with the primary goal of reproduction, sexual desire responds to
cues of reproductive readiness, such as physical markers of fertility
or status (Buss, 1994).

This evolutionary, attachment-related approach is best encapsulated
in Diamond’s (2003, 2004) biobehavioral model of romantic
love and sexual desire. Diamond argued that romantic love and
sexual desire serve different functions, namely to promote pair
bonding and sexual behavior, respectively. In support of these
claims, Diamond reviewed evidence showing that the subjective
experiences of romantic love and sexual desire are functionally
independent: Individuals can feel romantic love but not sexual
desire, or sexual desire but not romantic love, toward another
person. Romantic love and sexual desire, Diamond claimed, also
appear to be mediated by different physiological processes: oxytocin
(OT) and endogenous opioids in the case of romantic love,
and gonadal estrogens and androgens in the case of sexual desire. ..."